The present invention relates to a simple field installable/removable moisture and/or acid indicator or test kit, and more particularly, to a moisture and/or acid test indicator or test kit used in a vapor compression system and the like which can be attached to the system via an existing Schrader-type service valve making the indicator easily installed and/or replaced in the field, without the need to isolate a section of the system, recover the trapped refrigerant, install the indicator into the system, and recharge the section previously isolated and evacuated. The indicating material substance or formulation of the present invention is held in a transparent fixture which when tightened on the service valve, automatically depresses the Schrader valve core allowing refrigerant to contact the indicator material. This indicator can also be configured to magnify the section of the device which contains the indicator material. This allows technicians in the field to easily, simply, quickly and inexpensively attach a moisture or test kit, or change the test kit, on a fully charged and operating system without the need to interrupt operation of the system.
The presence of moisture in the refrigerant of vapor compression refrigerators, heat pumps, and air conditioners (generally referred to as, the system) can lead to the formation of ice crystals in the throttling device, thereby restricting the flow of refrigerant and decreasing capacity. The presence of water in such a system also accelerates the formation of acids in the system which severely shorten the life of both the compressor and the refrigerant.
All systems typically have service valves with valve core depressors (often referred to as Schrader-valves). These valves, like automobile tire-valves, are opened when a valve core is depressed, usually by the device being attached to the valve. For refrigeration systems, these types of service valves with valve core depressors are used in several standard sizes, with xc2xcxe2x80x3 being the most common and xe2x85x9cxe2x80x3, xc2xdxe2x80x3, and and ⅝xe2x80x3 also used.
Checking the system for moisture is a common maintenance procedure. Due to cost cutting measures, however, many systems do not contain a traditional moisture indicator in the system. When such a moisture indicator is inherent in the system it is typically located in the liquid line or in the liquid receiver as part of a liquid sight glass. Such indicators are configured for liquid refrigerant to flow through the device. Alternatively, U.S. Pat. Nos. 4,923,806 and 5,071,768, disclose a device which attaches to the service valve and allows refrigerant to flow through the device and into the ambient surroundings, indicating both moisture and acid as the refrigerant is vented to the environment. In addition to the obvious disadvantage of venting refrigerant into the environment, this device can not be installed for extended periods due to the constant flow of refrigerant being vented.
Visual sensors or indicators for use in detecting the moisture of a refrigerant in a vapor compression system are known, as seen for example, in U.S. Pat. No. 4,018,061 as well as in commercial products. A permanently installed sensor has a sight glass or window through which moisture content is determined by viewing a color-change indicator. Cobaltous chloride and cobaltous bromide are well known in the art as a moisture indicating chemicals, with the former changing from blue to pink when wet and the latter changing from green to yellow when wet.
Visual sensors or indicators for use in detecting the corrosive state of a fluid in a heat exchanger system are known as seen, for example, in U.S. Pat. No. 5,127,433. A permanently installed sensor has a sight glass or window through which corrosiveness or moisture content is determined by viewing a flap or ball displaying a color indicating either the need to change the fluid or to add corrosion inhibitors. Alternatively, corrosiveness can be indicated by a ruptured or broken diaphragm located between the sight glass and the fluid.
Humidity and corrosion indicators for packaged goods in which a thin cobaltous chloride film is used as the sensing element are discussed in U.S. Pat. No. 3,084,658. An elastomeric grommet sealed by a transparent disk is inserted into an opening in a package wall. A disk impregnated with the cobaltous chloride is secured beneath a window and can be replaced.
With respect to closed refrigeration systems, other types of indicator systems are known for testing the presence and concentration of contaminants in a refrigerant. For example, U.S. Pat. Nos. 4,923,806 and 5,071,768 show apparatus for testing liquid or vapor contaminants in a closed system regardless of whether or not the apparatus is operating. A disposable testing tube made of transparent material is used at the end of a compressor discharge line or elsewhere in the system. One section of the tube is provided with water removal and moisture indicating chemicals, such as cobaltous chloride and another section is provided with acid indicating chemicals such as a solution of bromophenol blue, ethanol and glycerol. This known construction is relatively complicated and requires a separate, specially configured flow restrictor in addition to a tube holder, and an expensive testing tube in which the multiple contaminant testing chemicals and filter screens are permanently located. U.S. Pat. No. 4,018,061 describes a moisture-indicating device in contact with flowing liquid refrigerant. This device is an integral part of the refrigeration system, and as such, the system must be shut down in order to install the device.
Likewise, U.S. Pat. No. 5,377,496 shows an acid contamination indicator for closed loop vapor compression refrigeration systems in which the indicator is permanently or removably installed in the bypass line around the system compressor where the refrigerant is always in the gaseous phase. A casing has a visual indicator bed of bromophenol blue as the acid indicating medium which is contacted by the refrigerant after flowing through a filter and a flow restrictor orifice. Porous retainer disks are held against the bed by springs. Moreover, the indicator, which changes color when exposed to acids or bases, are solid, and they must be exposed to the test stream in some fashion. Accordingly, this solid indicator must be mixed with an inert substance to provide some porosity, contact surface area, and increased volume and then packaged in a clear tube. The vapor refrigerant is then passed through the porous mixture arranged in a bypass loop between the suction and discharge ends of a compressor or in the main refrigerant flow path between the compressor discharge and a heat exchanger to observe a color change. Again, we have recognized that this is an unduly complicated construction which requires a substantial outlay for production and installation. A bypass of refrigerant from the compressor discharge to the compressor suction reduces the capacity and performance of the vapor compression system as well as increases the compressor operating temperature since hot discharge vapor is reintroduced into the compressor suction.
Pending U.S. patent application Ser. No. 08/423,211, filed Apr. 17, 1995, assigned to Mainstream Engineering Corporation of Rockledge, Fla. discloses yet another way of detecting the presence of acid in a refrigeration system, with an indicating device configured to temporally flow refrigerant through it and vent this refrigerant to the environment. The disclosure of that application is incorporated by reference herein.
Yet another type of contaminant detector is marketed by Refrigeration Technologies of Fullerton, Calif. under the trademark xe2x80x9cCHECKMATExe2x80x9d. A specific volume of gas passes through a detection tube at a predetermined termination pressure. However, a sealed Pyrex detection tube containing a color-changing chemical and having ends which are pierced when fully assembled can only be used once even when the test is negative, and thus this approach entails considerable expense regardless of its technical merits.
It should be pointed out that all the prior art for moisture or other contamination measuring devices, whether permanent or temporary, have one thing in common, namely an inlet and outlet so that refrigeration passes through the device. The refrigerant which passes through is (a) vented to ambient air or (b) by-passed to another portion of the system, or (c) the device is permanently placed in the refrigerant system""s normal flow path. We realized that due to cost saving measures, many air conditioning systems do not have a moisture indicator in the system, and it is expensive and disruptive to the unit""s operation, to retrofit such an indicator in the field.
In a vapor-compression system, refrigerant flows from the condenser to the expansion valve, where it flashes into a two-phase mixture and then enters the evaporator. Superheated refrigerant vapor, with some entrained oil, leaves the evaporator and is compressed in the compressor, before being condensed in the condenser to complete the cycle. The presence of water in the system, which is a very real possibility, can result in the formation of ice crystals as the refrigerant is throttled in the expansion device. Because the expansion device is a significant flow restriction, ice formed there can clog the flow path completely stopping the flow of refrigerant or severely reducing capacity. In addition to reducing system capacity, the ice formation can result in excessive pressures and system shut down. If this were to occur, the ice blockage would typically melt, allowing the system to restart and operate normally until the ice again formed. This overall result would be an on-off cycling of the device. Moisture can also accelerate the formation of corrosive acids in the system.
While we have looked at a temporary flow through indication device for moisture, the problem is compounded by the fact that the moisture levels attempting to be measured (at about 100 PPM or less) are significantly lower than the moisture level in ambient air. The costs associated with manufacturing a moisture indicator in this relatively wet environment and the false reading associated with exposing the indicator to ambient air before using, have led us to recognize a different solution to the problem. That is, a field installable temporary test kit device is used which does not begin as a dry indicator but rather begins at equilibrium with moisture in the air and therefore indicates wet conditions when first installed but after exposure to the refrigeration system reaches an equilibrium moisture concentration thereby indicating the level of moisture in the system.
Rather than constructing a device with an inlet and outlet that must be plumbed into the system (at a considerable cost), or one that must by-pass refrigeration in the system (thereby reducing performance and increasing compressor suction-side refrigerant temperature), however, we have configured a removable test kit with a single connection point which temporarily connects to the existing system service port (with only the tightening of a wrench in the case of a threaded service port, or by pushing it on, in the case of a quick disconnect type of service port.
Our device does not degrade system performance and can be quickly and easily installed. The action of attaching the indicator of the present invention to the service valve depresses the service valve""s Schrader valve, thereby allowing vapor refrigerant of the system to contact the indicator chemical. This is a particularly advantageous element of the present invention, because it affords the user with the benefits of a permanent moisture indicator, namely, sufficient time for the indicator to reach equilibrium moisture conditions (regardless of the starting moisture level), as well as the benefits of a low cost field-test device. That is, it can be used on an operating system without opening the system or disturbing its operation in any way.
The indicator housing of the present invention mechanism has a mechanism for depressing the Schrader valve core and a structure for holding an indicator material. The indicator formulation can be impregnated on a paper or porous plastic sheet or can be a paint applied to the interior surface of the cap. The moisture indicator material is prepared from an aqueous or solvent solution of finely divided particles of the indicator chemical and optionally polymers, and optionally other hygroscopic compounds. The paint is characterized by one color when in the absence of significant amounts of water and by a gradual color change to a second color with the presence of increasing quantities of water. The indicator housing is constructed of a clear material (or a material with a window), and can incorporate a magnifying glass (either manufactured into the clear material or into the window) so that the color change can be easily seen without a large quantity of the indicator material. This magnification is needed because the lower transport rates resulting from a vapor diffusion process require a smaller mass of indicator material compared with a flowing liquid system of the types described above to reach equilibrium moisture conditions in a practical time period.
Other known moisture indicators with an inlet and outlet, either temporary or permanent, have the moisture indicating material in the liquid stream of refrigerant, whereas the indicator of the present invention is located in a service valve fitting so that refrigerant (mostly vapor) does not flow through the device. Consequently, moisture must diffuse through the relatively stagnant area between the refrigerant flow path and the location of the indicator material. The smaller the mass of indicator material, the smaller the quantity of moisture that must diffuse before a complete reaction is achieved.
Because the mechanism of the moisture transport in the present invention is diffusion instead of flowing the refrigerant past the indicator material, an experiment was performed to verify that the diffusion of moisture from refrigerant into the adsorbent material could be accomplished in a reasonably short time. The experiment determined if diffusion of the moisture through static refrigerant would be rapid enough to be practical. Refrigerant samples were formulated with increasing quantities of moisture (ranging from 3 PPM water to 900 PPM in the liquid refrigerant). These samples were then exposed to moisture laden (pink) cobalt chloride-containing indicator materials, and moisture indicator observations were continued on a regular basis with time and indicator color recorded. Once the indicators had stabilized (remained the same color for a period greater than two days), the vapor and liquid were both tested for moisture by using a Karl Fisher coulometric titrator.
Although there is no generally accepted maximum permissible moisture limit on operating systems, a level of 125 ppm is an approximate upper limit for moisture concentrations in refrigerants found in systems (centrifugal chillers down to small unitary systems) operating for 10 years or more. We have also found through Karl Fisher titration that for refrigerants HFC-134a and HCFC-22 the percent by weight of water in the vapor phase relative to that in the liquid phase at equilibrium ranges from about 0.25-1, and is a function of temperature and the total concentration of moisture in the vapor/liquid system. This ratio is a thermodynamic property of the refrigerant and water system and can be very different for other refrigerants.
Results from this experiment indicate that the diffusion rates are sufficient, even in static conditions, to invoke a color change within a reasonable period of time (one day or less). To notice any color change in systems containing less than 100 PPM (parts per million) moisture in the liquid refrigerant, about one hour was required. After about fifteen hours, the color change was observed to be essentially complete (greater than 90% complete) for all moisture levels tested. Since the color change approaches an equilibrium in an exponential manner, a substantial (at least ⅔ color change) change can be seen within 8 hours. This degree of color change is clearly significant enough for a refrigeration technician to accurately diagnose a moisture contamination problem.
We have discovered that a device can be configured, either from a clear material or with a window, to contain a connection to the service valve, to depress the service valve, to hold the moisture indicating material, to magnify the moisture indication material so that a color change can be seen with a smaller mass of material, and a simple connection to an existing service port on the system so that the device can be attached without disturbing the system in any way. This temporary device can be easily removed when normal access to the service port is needed and can be easily changed when excessive moisture levels have made it no longer usable.
The device according to the present invention allows for testing with the system on or off. In addition, it does not have to be installed in a line but rather is temporarily or permanently connected to existing service connections, for example, to a Schrader-valve which is not directly in the flow path of the refrigerant. This is a surprising discovery because indicators are traditionally located in the liquid flow path or if connected to a vapor service valve vent to ambient or to another part of the system so as to have refrigerant flow through the device.
Specifically our invention currently contemplates use of an indicator chemical such as cobaltous chloride (CoCl2) or cobaltous bromide (CoBr2). CoCl2 will hydrate with six water molecules changing from blue color to pink color. CoBr2 will hydrate with six water molecules changing from green color to yellow color. There are also other chemicals which change color upon hydration including copper sulfate and other cobalt compounds. Certain alkali metal ozonides also change color. Acid-base reactions can also be used in conjunction with proper indicators in the presence of water.
Thus, the present invention takes advantage of the difficulty of normally attaching a permanent indicator into the plumbing of a existing (working) system and the cost and inconvenience of using a temporary indicator which vents or by-passes refrigerant to achieve the necessary flow through the indicator.
While many commercial moisture indicator chemicals are available, the preferred embodiment of this invention will use CoCl2 as the moisture indicator chemical. If the moisture concentration is not enough to turn the indicator completely pink, however, an intermediate color, between blue and pink (pale, almost while) will be observed. Therefore, the intensity of the change depends on what percentage of the indicator has been transformed (reacted) to the wet form. If the CoBr2 indicator is used a wet environment will produce a yellow color, where as in a dry environment the indicator chemical will appear green. If the moisture concentration is not enough to turn the indicator completely yellow, however, an intermediate color, between green and yellow (that is some yellowish shade of green) will be observed. Therefore, the intensity of the color change depends on what percentage of the indicator has been transformed (reacted) to the wet form.
Hygroscopic modifiers can also be added to the moisture sensing formulation in order to increase or decrease the sensitivity of the device to moisture present in the refrigeration system working fluid. These materials can include hygroscopic compounds such as copper sulfate, zinc chloride, calcium chloride, and silica gel or polymers which absorbs certain levels of moisture such as cellulose acetate, cellulose acetate butyrate, polyvinyl alcohol, and polyamide polymers.
It is, therefore, an object of the present invention to provide an accurate, yet simple and inexpensive, test device which can indicate the refrigerant""s moisture and/or acid level by contact with refrigerant vapor from existing system service valves, without the need to flow the refrigerant through the device, to provide an indication of the condition of the refrigerant and therefore the condition of the system.
The present invention advantageously uses a readily available, inexpensive indicator held in a transparent cap-like fixture to monitor the moisture and/or acid level. The indicator chemical reaction is essentially a function of moisture and/or acid level because the indicator material is kept in place until equilibrium conditions are reached. The present invention attaches to a standard refrigeration service valve with or without a valve-core depressor (Schrader-valve).
For automotive air conditioning applications, moisture and/or acid problems also exist. In fact, because of the frequent refrigerant recharging of automobile systems, the moisture problems are even worse. The present invention can also be used in those applications; however, the service port on newer automobiles is not threaded but rather uses a quick disconnect which by EPA Clean Air Act regulations is different for each refrigerant being used in an automobile application. The high-side and low-side ports are also different to avoid confusion by the technician or equipment owner. The indicator device of the present invention can be configured to securely attach to these different fittings (reference Fitting Sizes for Motor Vehicle Refrigerants June 1997, EPA-430-F-97-067).